1. Field of the Invention
This invention relates to a method and apparatus for measuring the force applied to a seat belt. Specifically, a sensor arrangement is mounted within a seatbelt anchor assembly to provide accurate seatbelt force measurements.
2. Related Art
Most vehicles include airbags and seatbelt restraint systems that work together to protect the driver and passengers from experiencing serious injuries due to a high speed collision. It is important to control the deployment force of the airbags based on the size of the driver or the passenger. When an adult is seated on the vehicle seat, the airbag should be deployed in a normal manner. If there is an infant seat secured to the vehicle seat then the airbag should not be deployed or should be deployed at a significantly lower deployment force. One way to control the airbag deployment is to monitor the weight of the seat occupant.
Current systems for measuring the weight of a seat occupant are complex and expensive. One type of system uses pressure sensitive foil mats mounted within the seat bottom foam. Another system uses sensors placed at a plurality of locations within the seat bottom. The combined output from the mats or the sensors is used to determine the weight of the seat occupant. If the sensors become damaged or fail to operate for some reason, the system will not provide accurate seat weight measurements and airbag deployment could occur under undesirable conditions.
Also mounting sensor systems within the seat can be difficult and time consuming. It is difficult to find mounting locations for each the sensors that will accommodate all of the various positions of a seated occupant while still providing accurate measurements. Further, shifting of the occupant on the seat can dislodge or move the sensors out of their proper location. Because the sensors are mounted within the seat bottom, it is difficult to reposition the sensors after the seat is installed in the vehicle.
Current sensor systems also can have difficulty determining whether an adult is belted to the seat or whether a child car seat is belted to the seat. When a child seat is in place, an excess acts on the sensors mounted within the rear portion of the seat, which interferes with accurate sensing of the weight of an occupant. Overtightening of the seatbelt, which makes it pull down on the rear of the seat, causes this force. Due to this effect, the current weight sensing systems have difficulty in discering between an adult and a child in a child seat.
Thus, it is desirable to have a system for determining whether conditions are proper for deploying an airbag by determining whether a child in a child seat or an adult is belted to the seat. The system should further provide accurate measurements, be easy to install, and should overcome the above referenced deficiencies with prior art systems.
In a disclosed embodiment of this invention, a system for measuring seatbelt forces includes a seatbelt anchor mounted to a vehicle structure adjacent to a vehicle seat and a seatbelt for securing an occupant to the vehicle seat. The seatbelt has a belt portion supported by the anchor. A sensor is engaged with the anchor for measuring the magnitude of forces exerted on the seat belt.
In a preferred embodiment, the seatbelt anchor is comprised of a bracket having a first portion with an opening for receiving the belt portion and a second portion for attaching the bracket to the vehicle structure. An airbag controller is used to control deployment of an airbag that is mounted within the vehicle near the seat. The sensor generates a signal representative of the seatbelt forces and transmits the signal to the controller. The airbag is prevented from deploying if the signal exceeds a predetermined limit.
The system includes at least one fastener that secures the anchor to the vehicle structure. Preferably, the sensor has a portion mounted between the fastener and the anchor.
A method for controlling airbag deployment includes the following steps. A seatbelt assembly is mounted adjacent to a vehicle seat with a seatbelt anchor. A force signal representative of forces applied to the seatbelt is generated via a sensor mounted to the seatbelt anchor. Deployment of an airbag is controlled based on the force signal. Preferably, deployment of the airbag is prevented if the signal exceeds a predetermined limit.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.